Electric pulse generating apparatus

ABSTRACT

In an electric ignition circuit for an internal combustion engine having a cam-like member of a magnetic material operatively connected to move as a function of engine speed, apparatus for generating electric pulses comprises a core member of magnetic material mounted with pole pieces formed by exposed faces of the core member adjacent said cam-like member and a coil wound round said core member connected to a direct current source for controlling magnetic flux in said core member and for deriving an electric pulse in accordance with the flux change in said core member brought about by the core member being driven into and out of magnetic saturation on movement of the cam-like member past said pole pieces.

United States Patent 11 1 1111 3,889,650 Rivers 1 1 June 17, 1975 1 ELECTRIC PULSE GENERATING 3,328.614 6/1967 Falge ct a1 123/148 E APPARATUS 3,370,190 2/1968 Neapo1itakis1 123/148 E 3.390.669 7/1968 Hufton t 123/148 E 5] In n r: Robert h t Rivers, OXIed, 3473.061 10/1969 Soehner et a]. 123/148 E England 3,550,572 12/1970 Walker 123/148 E I 3,554,179 1/1971 Burson v 123/148 E 173] Asslgneeg i f g' I 5 3,675,635 7/1972 Graser et a1 .1 123 148 E x e urrey, ng an [22] Filed: Dec. 15, 1972 Primary Examiner-Manuel A Antonakas I Assistant Examiner10seph A. Cangelosi 1211 Appl 3l5432 Attorney, Agent, or Firm-Brisebois & Kruger [30] Foreign Application Priority Data [57] ABSTRACT Dec. 15. 1971 United Kingdom 58258/71 June 8' 972 United Kingdom n 26783/72 In an 1CIHC lgmtlon c1rcu1t for an mternal combustion engine having a cam-like member of a magnetic 52 us. (:1. 123/148 E- 123/1465 material operatively CO'meCed as a fmcl'lo" [51] Int. Cl. F02p 1/00 of engine speed apparaws for generating electric [58] Field of Search 123/148 148 P1115 comprises a core member 0f magnelic mounted with pole pieces formed by exposed faces of [56] References Chad the core member adjacent said cam-like member and a coil wound round said core member connected to a UNITED 'jT PATENTS direct current source for controlling magnetic flux in 3.020.897 2/1962 Sek1n1 et a1. 123/148 E said core member and for deriving an electric pulse in gj E accordance with the flux change in said core member 3ZO34I2 8/1965 g g 123/148 E brought about by the core member being driven into 3219'878 H965 jjj: 123/148 E and out of magnetic saturation on movement of the 3,253,185 5/1966 Morrison. 123/148 E Cam-like member P said P P 3,277.875 10/1966 Miki 123/148 E 3.291,]08 12/1966 Schneider et a1 123/148 E 2 Cmms 5 Drawmg F'gum PATENTEUJUN 17 m5 SHEET FIG FIG. 3

FIG 5.

1 ELECTRIC PULSE GENERATING APPARATUS This invention relates to apparatus for generating electric pulses in accordance with the movement of a moving member. One form of apparatus in accordance with the invention is especially suitable for use in electrical ignition apparatus for internal combustion engines, and it is convenient to describe the invention in relation to this use.

Ignition circuits for external combustion engines are known in which semiconductor devices are used to generate high voltage pulses timed in accordance with the operation of mechanically actuated switch contacts, such as the conventional contact breaker. The high voltage pulses can be produced by, for example, capacitor or inductor discharge arrangements or by high frequency type generators.

It is desirable to be able to dispense with the mechan ically operated contacts, and suggestions have been made of ways in which this might be effected using for example photo-electric or inductive devices, but such proposed arrangements have had various disadvantages mitigating against their adoption in practice amongst which is the fact that the position at which the pulse which they produce occurs at points which vary with engine speed.

Because of the large number of motor vehicles in use which employ ignition circuits with conventional contact breakers, it is also desirable that any devices intended to replace such contact breakers should be adaptable for use with existing ignition circuits as far as possible.

It is an object of the present invention to produce an electric pulse generator which overcomes or at least mitigates the disadvantages of the known devices and produces a well defined pulse at a substantially constant point regardless of engine speed.

The present invention provides a pulse generator for generating electric pulses in accordance with the movement of a movable member of a magnetic material comprising a magnetic core member, means for mounting said core member adjacent the movable member, a coil associated with the core member, and means for connecting said coil to a direct current supply such that said core member is adapted to be driven into and out of magnetic saturation as the reluctance of the magnetic core member varies in accordance with the position of the movable member.

Features and advantages of the invention will appear from the following description of embodiments thereof, given by way of example, in conjunction with the accompanying drawings, in which:

FIG. I is a side elevation view of a pulse generator;

FIG. 2 is an end view of the generator of FIG. 1;

FIG. 3 is a plan view showing a pulse generator of the type shown in FIGS. I and 2 mounted in position adjacent the cam of a conventional contact breaker;

FIG. 4 is a pulse shaping network for use with a generator as shown in FIGS. 1 to 3; and

FIG. 5 is a side elevational view of another embodiment of a pulse generator.

The pulse generator shown in FIGS. I to 3 comprises a U-shaped magnetic core 10, composed of thin laminations of high permeability magnetic material such as that available under the trade marks mu-metal, or radio metal, In the embodiment shown, three such U-shaped laminations are used, but other configurations and numbers of laminations are possible. It is however desirable, for a reason which will appear that the end edges 10a and 10b of each of the laminations are aligned. A coil 11 is wound upon a bobbin 12 which fits on one limb of the assembled laminations.

The magnetic core, with the winding in position is mounted upon a carrier 13, shown diagrammatically in FIG. 3; the carrier is constructed so that it may replace the standard contact assembly of a conventional contact breaker actuated by a cam 14. The cam will normally have as many lobes as cylinders in the associated engine and is made of steel. The carrier 13 is provided with a slot whereby adjustment of the spacing between the core 10 and the cam 14 can be effected.

The carrier 13 is adjusted in use until there is only a small minimum clearance, of the order of 0.005 to 0.0l5 inch, preferably about 0.010 inch, between the edges 10a and 10b of the magnetic core and the cam lobes. As the cam rotates so will the gap between the core and the cam vary between the minimum given above and a greater value.

It is arranged that a constant direct current is fed through the winding 11, this current being of a value such that when the cam to core spacing is a minimum the reduction of the reluctance of the magnetic path presented by the core and the adjacent cam magnetically saturates the magnetic material of the core, but when the cam to core spacing increases, the material comes out of saturation. As the cam rotates the core material will go into and out of magnetic saturation and in consequence the voltage developed across the coil will show a marked change at the transistion point from saturation to non-saturation. This voltage has been found to be very suitable for controlling a timing pulse, and in a typical case has a waveform shown in the inset waveform diagram in FIG. 4. The voltage waveform rises to a peak value, followed by a sharp well defined drop in value as the magnetic core passes through the transistion between saturated and non-saturated conditions. The peak value of voltage varies, with speed, but the transistion point is constant. In practice, when the pulse generator is fitted to an existing distributor for an engine as a replacement for the contact breaker, the fact that the position of the transistion point is constant regardless of the speed of the cam is advantageous.

It is a disadvantage of certain types of pulse produc ing devices such as those of the inductive pick-off type that the effective triggering point in the cycle of operation of the engine varies with engine speed.

FIG. 4 shows a suitable circuit for energising the winding II with constant current and producing an output pulse of constant amplitude and duration, suitable for triggering an ignition device of the character referred to. The circuit is for a negative earth system; it can be modified in the usual manner for a positive earth system.

In FIG. 4 components R1, R2 etc. are resistors, CI, C2 etc. capacitors, TRl, TR2, transistors and Z1, 22 etc. zener diodes. In the circuit, a direct current supply at terminals 20, 21 which may be in this example between 5 and 16 volts, is filtered by R1 and C1; the constant current supply for winding 11 includes C2, Z1, R3, TRl and R2. The voltage appearing across the winding of the waveform somewhat as shown, is filtered by C3, R5, C4, R6 and C5 and applied through C6 to the base of TR2. TR2 has a collector load R8, and is stabilised by R7 and the collector supply is stabilised by R4 and Z2. TRZ is A.C. coupled through C7 and R9 to the input of a monostable circuit including R12, TR3, R13, R10, R11, TR4, R14, R15, TRS and R16 connected as shown. The output is taken from the collector of TRS and consists of a succession of pulses each of approximately 300 microseconds duration and an amplitude of about volts. The wavefront is steep, with a slope of about 10 volts/microsecond. Component values are marked in FIG. 4.

The device described can be used to produce pulses generally where the magnetic conditions of the core of the detector device can be varied, but is especially suitable for replacing the conventional contact breaker in an electronic ignition circuit. A practical form of the circuit of FIG. 4 has been found to be very satisfactory having characteristics stable with temperature and engine speed. The power for the pulse generator when used in a car is conveniently supplied by a battery having a nominal voltage of 12 v. This nominal voltage is reduced however when a starter motor, also supplied from the battery, is actuated. Other factors which affect the voltage actually supplied from the battery are the age of the battery and its temperature. The circuit will function properly with supply voltages much below the nominal voltage, giving good operation on starting, with an old battery or under cold ambient conditions.

It has been found, however. that from time to time, in certain installations, the erratic operation of the pulse generator can arisev It has been discovered during trials that such erratic operation can be induced in an installation where the electrical equipment on the engine or vehicle on which the pulse generator is used can give rise to large magnetic fields and that such fields may affect the magnetic conditions of the pulse producing means. For example, the heavy currents passing through a starter motor supply cable can give rise to a magnetic field which, by magnetising the largely magnetic parts of the engine, can produce a substantial field strength at the pulse generator.

To overcome this erratic operation, means for a protecting the magnetic pulse generator against the effects of stray magnetic fields can be provided. A variety of ways can be adopted for this purpose, but the method which is preferred since it is effective in operation and adds little to the manufacturing cost, is to provide a magnetically balanced system for the pulse generator.

In FIG. 5, there is shown diagrammatically another embodiment of a pulse generator using such a magnetically balanced system. This comprises a magnetic member 31, conveniently comprising a few laminations of high permeability magnetic material, for example the materials already disclosed, having two substantially similar parallel limbs 31A and 318, which terminate in pole faces 32A and 328. On the two limbs of the core are arranged coils 33 and 34 respectively and the coils are connected, conveniently in series, so that when a current is passed through the coils, they will be flux-aiding in the core member 31. The core member is mounted, conveniently in the manner described previously adjacent the conventional cam member 35 of an engine, The pulse generator will operate, in the manner described previously, to produce well-defined pulses which are then shaped and used to drive an ignition circuit, by means including the conventional distributor and a pulse transformer, which may be a conventional ignition coil.

However, while the two coils 33 and 34 are series aiding for the useful flux, they will be in opposition for a magnetic flux which passes through both coils in the same direction, as would be the case with a stray magnetic field. The two coils are arranged to have the same or substantially the same number of turns, so that the induced voltages will be substantially equal and oppo site. In this way, the effects of the stray magnetic field can be largely reduced or eliminated, giving rise to consistent operation. While one coil has been described for supplying current to the magnetic core member and for producing the pulses when the core member goes into and out of magnetic saturation, an alternative arrangement is for two coils to be provided, one for supplying current to the magnetic core and one for producing the pulses.

The above described pulse generator can be used for timing the operation of injectors for an engine having a fuel injection system in addition to or instead of timing the ignition of the engine.

Another convenient use for the pulse generator is with a capacitor discharge ignition system in which the battery voltage is amplified to a high voltage e.g. 400 V, and supplied to a capacitor. The pulse generator in this case supplies timing pulses for triggering the dis charge of the capacitor through the primary winding of a pulse transformer.

I claim:

I. In combination with an internal combustion engine, an electrical ignition circuit including a cam-like member of a magnetic material operatively connected to move as a function ofengine speed and apparatus for generating electric pulses, said apparatus comprising,

a core member of a magnetic material;

pole pieces formed by exposed faces of said core member;

means for mounting said core member with said pole pieces adjacent said cam-like member; a coil wound round a portion of said core member for controlling the magnetic flux in said core member;

circuit means operatively connected to said coil for supplying said coil with a direct current of such a magnitude that said core member is driven into and out of magnetic saturation on movement of the cam-like member past said pole pieces; and

desaturation detection means for deriving an electric pulse when said core member is driven from a saturated to a desaturated condition.

2. Combination according to claim 1 wherein said circuit means for supplying said coil with a direct current includes means for supplying a direct current of essentially constant magnitude to said coil. 

1. In combination with an internal combustion engine, an electrical ignition circuit including a cam-like member of a magnetic material operatively connected to move as a function of engine speed and apparatus for generating electric pulses, said apparatus comprising, a core member of a magnetic material; pole pieces formed by exposed faces of said core member; means for mounting said core member with said pole pieces adjacent said cam-like member; a coil wound round a portion of said core member for controlling the magnetic flux in said core member; circuit means operatively connected to said coil for supplying said coil with a direct current of such a magnitude that said core member is driven into and out of magnetic saturation on movement of the cam-like member past said pole pieces; and desaturation detection means for deriving an electric pulse when said core member is driven from a saturated to a desaturated condition.
 2. Combination according to claim 1 wherein said circuit means for supplying said coil with a direct current includes means for supplying a direct current of essentially constant magnitude to said coil. 